[tom406]

It is hard to find a definitive answer to this question. My old copy of "How To Restore Your Mustang-By the editors of Mustang Monthly Magazine" published in the 80s has a color scheme paint chart that shows the following for D7:
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Group 1 (Parchment #5779) Standard Interior-instrument panel, steering column, steering wheel, kick panels, windshield post, sun visors, metal door surfaces, quarter trim panels, console, 2+2 overhead moulding, Rally Pac.

Group 2 (Med Aqua Irid #5751) Standard interior-crash pad, radio speaker grille, lower windshield moulding, door panel, arm rest pad.

*Seat belts and carpeting are color keyed to Group 2 appointments.
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That said, I wouldn't be surprised if Parchment seat belts were substituted when aqua was not available or in short supply.

Good luck,
TOM